Releasable coupling

ABSTRACT

A coupling for releasably engaging a tubular member has a hollow body, in which the tubular member is received, and a sleeve which is movable axially within the hollow body. The sleeve is provided with an array of spacially separated holes and rotatable gripping members are located in these holes for selectively engaging the outer surface of the tubular member. During insertion of the tubular member into the hollow body, the rotatable gripping members move away from the outer surface of the tubular member. Movement of the tubular member in the opposite direction causes the rotatable gripping members to be cammed into contact with the surface of the tubular member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to couplings in which a hollow body isadapted to grip and retain an object inserted into it, with the grippingeffect being releasable such that the object may be removed from thebody.

In particular, the invention relates to devices in which the attemptedremoval of the object from the body without operating a releasemechanism causes a gripping device to engage and grip the object moretightly, so that removal of the object is prevented.

2. Description of the Prior Art

An example of such a releasable coupling has a resilient washer having aplurality of resilient fingers located near the entrance to the body.The resilient fingers extend into the hollow body in a direction awayfrom the entrance and are oriented at an acute angle to the body'sinternal surface, so that a tube may be inserted by pushing it past thefingers, but removal of the tube is prevented by the gripping effect ofthe fingers as they are forced to bend outwards. The tube may be removedby pressing a ring, for example, which acts on the washer to bend thefingers away from the tube surface, thus releasing their grip on thetube and allowing its removal.

Such prior art devices using a washer with internally facing resilientfingers have been found to have a number of problems. Firstly, they relyon the resilience of the fingers to provide sufficient initial grip onthe inserted tube so that the withdrawal of the tube is prevented by theeffect of pulling the tube from the socket tending to bend the fingerstowards the tube. Repeated use of the device will tend to reduce theresilience of the fingers, therefore weakening the gripping effect onthe tube and thus degrading the coupling's operation. If the angle ofthe fingers to the axis of the tube when gripping it becomes too closeto the perpendicular, it may be possible to remove the tube by applyingsufficient force since the fingers can more easily be bent in thisposition. Once this has occurred, the device may be permanently damaged.There is also a risk that because the tube must be forced past theresilient fingers as it is inserted, it or the fingers may becomedamaged. This can be particularly important if a good seal between thetube surface and coupling is required. Finally, since it is necessary tobend the fingers away from the tube surface in order to release thetube, there is also a requirement that the inserted tube must be able tobe moved at least a very small distance further into the socket in orderto lessen the gripping of the tube by the fingers so that this can beachieved. Thus if the tube has been inserted into the body as far aspossible, there may not be sufficient axial play for the tube to bereleasable.

Another prior art device, which does not use a washer having resilientfingers, thus overcoming some of the problems mentioned above, isdescribed in GB-1520742. This document discloses a tube coupling havinga cylindrical hollow body in which a collet may be inserted from the endin which the tube is to be inserted. The collet has inwardly taperingresilient arms which extend into the body away from the opening throughwhich the tube is inserted. The collet is free to move axially withinthe body, and a cam surface is provided on the body near the entranceand is arranged such that attempted removal of the collet past thissurface forces the resilient arms inwards towards the centre of thebody. Thus, when a tube is inserted, this forces the resilient arms ofthe collet apart, but attempted removal of the tube brings the arms intocontact with the cam surface, causing them to grip the tube moretightly. The arms grip the tube due to their resilience and are thuscarried with it. By pushing the end of the collet which protrudes fromthe entrance of the body towards the body, the resilient arms areprevented from coming into contact with the cam surface, and are free tospread slightly, and thus the tube can be removed.

An improved version of the GB-1520742 device is described inGB-B-2165604. This improved device still uses resilient arms to grip thetube, but metal teeth are provided on the inside surfaces of the arms toimprove this grip. Two O-rings are also used to seal the tube in thecoupling more efficiently.

Although these devices using a collet having inwardly tapering resilientarms to grip the tube avoid some of the problems associated withwashers, they still rely initially on the resilience of a member to gripthe tube, so repeated use can degrade their performance. Again, damagecan occur to the tube or collet as the tube is inserted past theresilient arms. If the collet is intended to be removable from thesocket, such that it is replaceable for example, then the removal of thecollet past the cam surface forces the arms to flex a relatively largedistance inwardly, thus again subjecting them to relatively largedeformations.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided areleasable coupling for retaining an object inserted through an openingin one end of a hollow body, comprising: retaining means for engagingand gripping said object, said retaining means being arranged such thatsaid object may be inserted into said body past said retaining meanssubstantially without resilient deformation of the retaining means, andsuch that removal of said object is substantially prevented by thegripping action of said retaining means; and release means for releasingthe gripping action of said retaining means to permit withdrawal of saidobject from said body.

In the present invention, since the object may be inserted withoutresilient deformation of the retaining means, the build-up of damage dueto repeated deformation, and the degradation in performance of theretaining means does not occur.

Preferably, the retaining means is arranged such that the object may beinserted substantially without resistance. In that case, there issubstantially no deformation of either the object being inserted, theretaining means, or the hollow body. Thus there is no risk of damagebeing caused by any forces acting as the object is inserted, nor ofrepeated insertions causing a build-up of such damage.

The coupling device of the present invention is suitable for use inbasic plugs and sockets, such as electrical plugs and sockets. It isalso useful for coupling pipes, in which case the hollow body would havea throughbore. Both metal and plastic pipes can be coupled, and evensoft walled tubes can be used provided a more rigid central support coreis inserted within the tube prior to insertion in the coupling. Thiscore could be, for example, separable from the coupling, or a captivespigot therewith.

The retaining means is preferably arranged such that attempted removalof the object through the opening causes the retaining means to grip theobject more tightly.

In a preferred embodiment, the retaining means is free to movesubstantially without resistance at least a small distance in adirection substantially perpendicular to the longitudinal axis of thebody, but is adapted such that the contact in use between the outersurface of the object and the retaining means generates sufficientfrictional force for movement of the object towards the opening in thebody to entrain the retaining means.

The freedom of the retaining means to move in a direction perpendicularto the longitudinal axis of the body means that substantially noresistance is provided to the object's insertion, since the retainingmeans may freely move apart to accommodate it. Furthermore, since theretaining means is correspondingly free to move towards the longitudinalaxis of the body (i.e. the object surface), resilient deformation ofpart of the retaining means or body is not essential to grip the object.There is also no dependence on the resilient deformation of a member togrip the object initially, since the frictional contact between theobject surface and the retaining means is sufficient to entrain theretaining means. The retaining means can also accommodate variations inthe width of the object, and is not constrained to be a suitableresiliently deforming member.

The gripping action of the retaining means on the object may be providedby a cam surface located on the inside of the hollow body and arrangedto engage the retaining means as it is moved axially towards theopening. The cam surface is arranged to cause the retaining means tomove towards the axis of the body, thus the attempted removal of theobject entrains the retaining means and causes it to engage the camsurface and thus grip the object.

The release means preferably acts to prevent the retaining means fromengaging the cam surface, or moves the retaining means out of engagementwith the cam surface, so that the object may easily be removed. To dothis, the release means may be arranged such that it may move theretaining means in an axial direction away from the cam surface.

In a preferred embodiment of the present invention, the release meanscomprises a hollow sleeve for receiving the object which is adapted tofit snugly within the hollow body and to move axially therein, and hasone or more holes located around its circumference, preferably at thesame axial position. The retaining means comprises one or more grippingmeans adapted to engage and grip the object, which may be placed in theholes in the sleeve so as to protrude into the hollow body so that theyengage the object surface and will not fit past the cam surface whendoing so. Preferably, the gripping means and holes are arranged suchthat the gripping means may move in the holes radially away from ortowards the longitudinal axis of the body, but cannot move in an axialdirection independently of the sleeve. Thus axial movement of the sleeveinto the body entrains the gripping means and will move them out ofengagement with the cam surface, releasing the gripping effect. Thenumber of gripping means located around the circumference of the sleevecan be varied. Six has been found to be a suitable number. Since in thisembodiment the retaining and release means are physically separate, theymay be constructed of different materials and thus adapted to a givendesired use.

The use of an axially moveable sleeve carrying freely floating grippingmeans within the hollow body is a particularly efficient and easy toconstruct arrangement for both gripping the object and allowing it to bereleased.

The hollow body preferably comprises a narrower diameter sectionextending from the opening through which the object is inserted to agiven axial depth into the body, followed by an increased diametersection in which the gripping means carried by the sleeve are locatedwhen the coupling is assembled. A tapering section is located betweenthe two different diameter sections and acts as the cam surface. In thisconstruction the gripping means are free to move apart away from thelongitudinal axis of the body when in the larger diameter section sothat the object may be inserted, but upon attempted removal of theobject, the friction between the gripping means and object surfacecauses the gripping means to be moved such that they come intoengagement with the cam surface which prevents further axial movement ofthe gripping means out of the body and forces them inwards to grip theobject more tightly, thus preventing its removal. In contrast toattempted removal of the object, insertion of the object will entrainthe gripping means away from the cam surface into the larger diametersection if they are not already there, thus allowing the object to beinserted easily.

The cam surface is preferably grooved. This increases its action on thegripping means.

The sleeve preferably extends beyond the opening of the hollow body,such that force may be applied on it to move it into the body in orderto hold the gripping means out of contact with the cam surface,therefore allowing removal of the object. The sleeve may also be pushedinto the body by a user when inserting the object to move the grippingmeans away from the cam surface when necessary, instead of simplyallowing the friction between the object surface and gripping means todo this, if desired. A flange may be provided on the external part ofthe sleeve to aid a user in pushing it in a direction into the body. Thesleeve may be resiliently biassed in an axial direction out of theopening in the body, such that a positive action is required to releasethe gripping means and remove the object, thus preventing accidentalremoval.

The sleeve and gripping means are preferably arranged such that when noobject is inserted therein, the gripping means can move sufficientlyinwardly towards the longitudinal axis to allow them to pass through thenarrower diameter section of the hollow body. This allows the couplingto be simply assembled by inserting the sleeve with the gripping meansinto the opening through which the object is to be inserted, therebysimplifying the construction of the coupling. A small lug may beprovided on the outer surface of the sleeve to retain the sleeve in thebody once assembled.

In a particularly preferred embodiment, the gripping means compriserotatable members such as rollers or balls balls for engaging thesurface of the object. These members may have a plurality of teeth ontheir external surfaces to increase their gripping action. The rotatablemembers may be supported on the sleeve such that they are free torotate, with their axes of rotation substantially perpendicular to thelongitudinal axis of the hollow body.

The use of rotatable members is especially advantageous because theirrotation brings different parts of their surfaces into contact with theobject for any given insertion. There is, in effect, therefore areplenishable surface for gripping the object, since should any part ofthe surface of the rotatable members become too worn, rotation of themember will bring a new part of the surface into contact with the objectsurface. If teeth or serrations are provided on the rotatable members,then these are effectively continuously replaced as the members rotate.This is contrast to the prior art, for example the device inGB-B-2165604, in which the same surfaces, or teeth, if provided on theinsides of the resilient arms, are in contact with the object's surfaceevery time, so that once these surfaces or teeth have become worn, theoperation of the device is impaired. Rollers are especially suitable foruse in a coupling for hard pipes, such as metal piping, and balls areespecially suited to soft deformable pipes.

The present invention therefore also extends to a releasable couplingfor retaining an object inserted through an opening in one end of ahollow body, comprising: retaining means for engaging and gripping saidobject, said retaining means being arranged such that said object may berelatively easily inserted into said body past said retaining means, andsuch that removal of said object is substantially prevented by thegripping action of said retaining means; and release means for releasingthe gripping action of said retaining means to permit withdrawal of saidobject from said body; wherein said retaining means includes one or morerotatable members adapted to engage the surface of said object, wherebydifferent parts of the member surfaces may be brought into engagementwith the surface of said object to assist retention of the object.

An alternative gripping means consists of triangular or rectangularcross-sectioned wedges, which have large flat faces having a largenumber of teeth thereon in contact with the object surface. These areespecially suitable for use with softer objects, such as plastic piping,since there is a greater surface area of teeth in contact with theobject at any given time, thereby improving the grip. Another suitablegripping means which can be used with a deformable pipe surface is aball such as a plastic ball. In use the ball digs into the pipe surface,and the high surface of area of contact between the pipe and ball causessufficient friction to grip the pipe.

In a preferred arrangement for gripping a deformable pipe, an insert orcaptive spigot used as a central support core has longitudinal fluteswhich correspond to the position of gripping balls. The flutes can havecircumferential grooves such that when the balls meet the cam surface,they press the pipe into the flutes to be gripped by the grooves.

In the case of a high pressure pipe coupling, a circumferential groovecan be included on the pipe to be inserted, such that the gripping meansengage therein in use, thus strengthening the gripping effect.

For coupling fragile objects, such as glass tubes, the gripping meansare preferably deformable (although, they would not, of course, deformas the object is inserted, due to the design of the coupling of thepresent invention), for example rubber rollers. When gripping theobject, the gripping means in this embodiment will, deform, thusreducing the risk of damage to a fragile object which could occur withsubstantially rigid gripping means.

A seal, such as an O-ring, may be placed in the larger diameter portionof the hollow body, beyond the end of the sleeve, such that uponinsertion of the object into the O-ring (and some resistance may beencountered here), this ring is trapped and thus forms a fluid tightseal between the object and the body. This is especially applicable whencoupling pipes. This seal can also have the effect that if there is aback pressure due to fluid flowing in the pipe, then it may be pressedback to act on the sleeve and thus effectively the gripping means,thereby strengthening the grip on the object.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described by way of exampleonly and with reference to the accompanying drawings, in which:FIG.

FIG. 1 is a partially cut-away side view of the releasable coupling ofthe present invention;

FIG. 2 is an enlarged view of the cut-away portion of FIG. 1 showing thereleasable coupling; and

FIG. 3 is a schematic cross-sectional view in a plane perpendicular tothe axis of the releasable coupling.

DESCRIPTION OF THE DISCLOSED EMBODIMENTS

In FIG. 1 the releasable coupling is shown generally at 1. A pipe 2 isshown inserted therein such that it is locked in place by the coupling.The coupling 1 comprises a hollow outer body 3 for receiving the pipe 2.In the present embodiment, since the coupling 1 is being used to couplea pipe, it is also shown to have a hollow throughbore section to allowflow of fluid through the pipe and coupling. When the coupling is beingused in a plug and socket fashion, which does not require throughpassage of the fluid, etc., through the coupling, then the end of thehollow body 3 may simply be closed off.

The hollow body 3 has a larger diameter section 4, and an internalreducing taper leading towards the narrow diameter opening on which isprovided a grooved cam surface 5 which slopes inwardly towards the axisof the body 3 in a direction towards the opening of the body throughwhich the pipe 2 is inserted. The grooves may be machined or moulded onthe cam surface 5.

A sleeve 6 comprising a hollow tube adapted to fit snugly within thehollow body 3 is placed within the body such that at least part of itprotrudes beyond the opening in the body 3. The sleeve 6 is able to movein the direction of its longitudinal axis within the body 3.

Located around the circumference at a given axial position on the sleeve6 are a number of holes 7, and corresponding slots 8, in which grippingmeans 9 for gripping the pipe 2 are placed. The holes 7 pass completelythrough the sleeve 6 in a radial direction such that the gripping means9 are able to come into contact with the pipe surface 10. The slots 8are closed at the end closest the pipe surface 10 and are adapted tocarry the gripping means 9 such that they may move freely andindependently of the sleeve 6 at least in a radial direction(i.e.perpendicular to the longitudinal axis of the body, sleeve andpipe), but so that axial movement of the sleeve 6 entrains the grippingmeans 9 so that they move simultaneously therewith. The holes 7 andslots 8 are located at an axial position on the sleeve 6 such that thegripping means 9 are positioned in the larger diameter section 4 of thehollow body 3 once the coupling is assembled, but so that movement ofthe sleeve 6 in an axial direction out of the body 3 may bring them intoengagement with the cam surface 5.

In the present embodiment, the gripping means 9 are shown as rollers,with surfaces 11 which have been milled or otherwise machined to have anumber of sharp teeth or grooves thereon. Spindles 12 of the rollers arelocated in the slots 8 of the sleeve 6, as shown in FIG. 3, such thatthe rollers are free to rotate and to move in a radial direction withinthe slots 8. The gripping surfaces 11 of the rollers are located in theholes 7 and can thus come into contact with the surface 10 of the pipe2. The rollers are dimensioned such that when in contact with thesurface of a pipe 10, the gripping surfaces 11 will not pass beyond thecam surface 5.

In an alternative arrangement, the gripping means 9 can be strung on aretaining loop or circlip which passes through their longitudinal axesand encircles the sleeve 6 to retain the gripping means loosely inposition. In this arrangement the slots 8 and spindles 12 areunnecessary.

FIG. 3 shows the location of the gripping rollers 9 around thecircumference of the sleeve 6. The number of gripping means 9 may, ofcourse, be varied; six has been found to be a suitable number.

The sleeve 6 has an enlarged flange portion 13 on the end thereof whichprotrudes beyond the opening of the hollow body 3, to allow the user tomove the sleeve 6 along the axis of the hollow body 3, and thus thegripping means 9 towards and away from the cam surface 5.

An O-ring 14 may be provided in the larger diameter section 4 of thehollow body 3 beyond the end of the sleeve 6 to act as a seal when thepipe 2 is inserted.

The coupling operates in the following manner. As the pipe 2 is insertedinto the sleeve 6 (i.e. the hollow body 3), the gripping means 9 engageits surface 10 and are thus carried inwards, until the gripping means 9can move radially away from the surface 10 of the pipe such that theyopen enough to permit free entry of the pipe 2. It is, of course, alsopossible to press the flange 13 of the sleeve 6 towards the body 3 tomove the gripping means inwards so that they may move apart toaccommodate the pipe. When an attempt is made to withdraw the pipethrough the opening, friction between the gripping means 9 and thesurface 10 of the pipe 2 causes the gripping means (and thus the sleeve)to move in an axial direction therewith until they engage the camsurface 5. The action of the cam surface 5 on the gripping means 9causes them to attempt to move inwards towards the axis of the pipe 2,thereby gripping the pipe more tightly. Thus the more pressure exertedto withdraw the pipe, the greater the grip.

To release the pipe, it is necessary to prevent the axial movement ofthe gripping means 9 which brings them into contact with cam surface 5and hence with the pipe as it is removed. This is achieved by pressingthe flange 13 of the sleeve 6 in a direction into the hollow body, thusmoving the sleeve and hence the gripping means 9 in an axial directionaway from the cam surface 5, and positioning the gripping means 9 withinthe larger section 4 of the hollow body; the pipe 2 may then easily beremoved.

When the pipe is inserted, as shown in FIG. 2, the O-ring 14 is trappedbetween the surface 10 of the pipe and the inner surface of the housing3, thereby forming a seal. If there is a large back pressure of fluidtrying to force the pipe 2 out of the opening of the body 3, the O-ringmay be forced against the end of the sleeve 6, thus acting to force thegripping means 9 into stronger contact with the cam surface 5, therebyincreasing the gripping effect on the pipe.

A biassing spring 16 may be located in the gap 15 between the end of thehollow body 3 and the flange 13 of the sleeve 6, in order to bias theflange 13 in a direction away from the hollow body 3, thus biassing thegripping means 9 into contact with the cam surface 5. This biassingmeans may be for example an O-ring, or a spring washer. This biassing ofthe coupling in a locked position means that the pipe cannot beinadvertently removed, since to do so it is necessary to apply a forceon the flange 13 to overcome the biassing of the spring. A positiveaction is therefore required to release the pipe 2.

Although in the present embodiment the gripping means 9 have been shownas rollers, any other suitable form of gripping means, i.e. one whichhas a surface to grip the surface of the pipe 10 and a part which willbe engaged by the cam surface 5 when a pipe is inserted and attempted tobe removed may be used. For example, triangular cross-section wedgeshaving larger lower surfaces with a plurality of teeth thereon, orballs, may be more suitable for softer piping, since a greater surfacearea in contact with the pipe will increase the gripping action.

Similarly, although the present embodiment describes the use of thecoupling of the present invention for coupling pipes, it is in factsuitable for any type of device where it is desired to lock a plugwithin a socket, with the plug being relatively easily releasable. Itcould, for example, be used in everyday electrical plugs and sockets toprevent accidental removal of the plug from the socket.

Alternatively, the coupling of the present invention could be used toposition and assemble display stands, for example, since it can beplaced and held at any desired position on a continuous object passingthrough it, simply by releasing the coupling, moving it into positionand then allowing it to lock again. In a preferred arrangement twocouplings could be arranged back-to-back with a bore passing throughboth couplings, such that the couplings will lock for movement in eitherdirection along an object inserted in the bore, unless one of thecouplings is released. In a similar manner, the coupling can be used tocontrol the movement of a continuous object, for example as a ratchet ornon-return mechanism, as a brake, or as a clutch. The gripping meanscould be covered by a friction material for this application.

What is claimed is:
 1. A releasable coupling comprising:a hollow bodyfor receiving an object to be retained, said hollow body having alongitudinal axis and being sized and shaped to receive an object to beretained; an opening in one end of said hollow body through which anobject may be inserted into said body; retaining means within saidhollow body for engaging and gripping the outer surface of the objectonce it has been inserted, said retaining means being arranged such thatthe object may be inserted into said body past said retaining means, andsuch that removal of the object is substantially prevented by thegripping action of said retaining means; and release means for releasingthe gripping action of said retaining means to permit withdrawal of theobject from said body; wherein said retaining means includes one or morerotatable members adapted to engage the surface of the object, each ofsaid rotatable members having teeth, serrations or grooves which extendcompletely about the perimeter of an external surface of each rotatablemember whereby different parts of each member's external surface may bebrought into engagement with the surface of the object when inserted toretain the object in said hollow body.
 2. A coupling as claimed in claim1, wherein the retaining means is arranged such that the object may beinserted into said body substantially without resistance.
 3. A couplingas claimed in claim 1, wherein the retaining means is arranged such thatattempted removal of the object through the opening causes the retainingmeans to grip the object more tightly.
 4. A coupling as claimed in claim1, wherein said retaining means are free to move substantially withoutresistance a distance in a direction substantially perpendicular to thelongitudinal axis of the body sufficient to allow the object to beinserted into said body substantially without resistance, contactbetween the outer surface of an inserted object and said retaining meansgenerating sufficient frictional force during movement of the object ina direction opposite to the direction of insertion to cause said body toentrain said retaining means.
 5. A coupling as claimed in claim 1,wherein the gripping action of the retaining means on the object isprovided by a cam surface located on the inside of the hollow body andarranged to engage the retaining means as it is moved axially towardsthe opening.
 6. A coupling as claimed in claim 5, wherein the releasemeans acts to prevent the engagement of the cam surface and retainingmeans, whereby the object may easily be removed.
 7. A coupling asclaimed in claim 6, wherein the release means is arranged such that itmay move the retaining means in an axial direction away from the camsurface.
 8. A coupling as claimed in any preceding claim 1, wherein eachof the rotatable members are rollers.
 9. A releasable couplingcomprising:a hollow body, said hollow body defining an axis and beingsized and shaped to receive an object to be retained, the object havingan exterior surface; an opening in one end of said hollow body throughwhich an object to be retained may be axially inserted into said hollowbody; retaining means supported within said hollow body for engaging andgripping the exterior surface of an inserted object, said retainingmeans being arranged such that the object may be inserted into said bodypast said retaining means, and such that subsequent removal of theobject may be substantially prevented by the gripping action of saidretaining means; and release means for releasing the gripping action ofsaid retaining means to permit axial withdrawal of the object from saidbody; wherein said retaining means includes at least one rotatablemember adapted to engage the exterior surface of an object inserted pastsaid rotatable member, said rotatable member having an irregularexternal gripping surface which may be brought into gripping engagementwith the exterior surface of the inserted object to retain the object insaid body; and wherein the gripping engagement of the exterior surfaceof the object by said retaining means results from camming actionproduced by a grooved cam surface located on the inside of said hollowbody, said cam surface being arranged to engage said retaining means inresponse to axial movement of said rotatable member relative to said camsurface and in the direction of said opening.
 10. A coupling as claimedin claim 9, wherein said release means acts to prevent the engagementbetween said cam surface and said retaining means, whereby an insertedobject may easily be removed from said hollow body.
 11. A coupling asclaimed in claim 10, wherein said release means is arranged such that itmay move said retaining means in an axial direction away from said camsurface.
 12. A coupling as claimed in claim 9, wherein said retainingmeans comprises a plurality of said rotatable members, and wherein saidrotatable members comprise rollers.
 13. A releasable couplingcomprising:a hollow body, said hollow body having a longitudinal axisand being sized and shaped to receive an object to be retained, theobject having an exterior surface and a longitudinal axis; an opening inone end of said hollow body through which an object to be retained maybe axially inserted into said hollow body; retaining means positionedwithin said hollow body for engaging and gripping the exterior surfaceof an inserted object, said retaining means being arranged such that theobject may be inserted into said body past said retaining means, andsuch that subsequent removal of the object may be substantiallyprevented by the gripping action of said retaining means; and releasemeans for releasing the gripping action of said retaining means topermit axial withdrawal of the object from said body; wherein saidretaining means comprising a plurality of rotatable members for engagingthe surface of an object inserted past said retaining means, each ofsaid rotatable members having an irregular external surface wherebydifferent parts of said irregular external surfaces may be brought intoengagement with the exterior surface of an inserted object to therebyretain the object in said hollow body; and wherein the grippingengagement of the exterior surface of an inserted object by saidrotatable members results from camming action produced by a cam surfacelocated on the inside of said hollow body, said cam surface beingarranged to engage said retaining means in response to axial movement ofsaid rotatable members relative to said cam surface and in the directionof said opening; and wherein:said release means comprises a hollowsleeve adapted to fit snugly within said hollow body and to move axiallytherein, said sleeve having a plurality of holes extending therethrough,said holes being located about the circumference of said sleeve, each ofsaid rotatable members of said retaining means being located in arespective of said holes in said sleeve in such a manner that it is freeto rotate; said rotatable members and said sleeve being arranged suchthat said rotatable members protrude into said hollow body for engagingan inserted object, said rotatable members also extending from saidsleeve for engagement by said cam surface.
 14. A coupling as claimed inclaim 13, wherein each of said rotatable members and said sleeve arefurther arranged such that each rotatable member may move independentlyradially away from or towards the longitudinal axis of said body, but isentrained for axial movement with said sleeve.
 15. A coupling as claimedin claim 13, including six of said rotatable members.
 16. A coupling asclaimed in claim 13, wherein said hollow body comprises a diametersection extending from said opening through which the object isinserted, said first diameter section being followed by a seconddiameter section spaced from said opening, the diameter of said secondsection being greater than the diameter of said first section, saidrotatable members being located in said second diameter section whenengaged with an inserted object, said cam surface being formed by atapering section of said hollow body joining said first and seconddiameter sections.
 17. A coupling as claimed in claim 13, wherein saidsleeve extends axially beyond said opening of said hollow body.
 18. Acoupling as claimed in claim 17, wherein the sleeve includes a flange onits external part.
 19. A coupling as claimed in claim 13, wherein saidsleeve is resiliently biased in an axial direction out of said openingof said body.
 20. A coupling as claimed in claim 13, wherein said sleeveand each said rotatable member is arranged such that when no object isinserted in said body each of said rotatable members can movesufficiently inwardly towards the longitudinal axis of said body toallow it to pass out of said body whilst still being located in a saidhole in said sleeve.
 21. A coupling as claimed in claim 13, wherein saidrotatable members are rollers.
 22. A coupling as claimed in claim 13,wherein said cam surface is grooved.
 23. A coupling as claimed in claim13, wherein said release means acts to prevent engagement between saidcam surface and said retaining means, whereby an inserted object mayeasily be removed from said hollow body.
 24. A coupling as claimed inclaim 23, wherein said release means is arranged such that it may movesaid retaining means in an axial direction away from said cam surface.